THE EGS5 CODE SYSTEM

C.1 Introduction
PEGS (Preprocessor for EGS) is a set of FORTRAN subprograms which generate material data
for use with the EGS5 Monte Carlo shower code and which also provide utilities for researchers
studying electro-magnetic interactions. The active operations of PEGS are functionals; that is,
they are operations whose arguments are functions (the functions related to physics interactions).
Included among these operations are:
• Fitting of functions by means of piecewise linear fits.
• Production of printed plots of selected functions.
• Evaluation of functions at selected points.
• Comparison of functions with sampled spectra.
Associated with these active functionals are other operations:
• Selection of material to which the functions refer.
• Selection of energy cutoffs for fits.
• Printing of fitted data.
This manual describes the full general functionality of PEGS. Users interested only in preparing
data sets for EGS5 can proceed directly to section C.3.
C.2 Structural Organization of PEGS
Beginning with version 5 of the EGS code system, MORTRAN is no longer supported, and PEGS
is no longer a stand-alone program, but rather a subroutine to be called by EGS user code. The
main PEGS subroutine (called PEGS5), however is essentially the same as the MAIN program in
previous versions of PEGS, and EGS and PEGS are still quite distinct in EGS5.
The full PEGS5 system consists of almost 7000 of FORTRAN source code that make up over
100 subprograms, plus an additional 610 lines of FORTRAN in 40 files containing COMMON blocks
accessed by the various PEGS subprograms through include statements. New to version 5 of
PEGS, all floating point variables are declared as double precision.
Despite its size, PEGS has a simple structure. Figures C.1 and C.2 below contain a schematic
flowchart of main subroutine (PEGS5) of PEGS. After the once-only initializations, an option loop
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